80 METALLURGY OP IRON AND STEEL. *
power, or 450,000 B.t.u. per 24 hours. Assuming 60 per cent, efficiency in the boiler plant, each engine horse-power calls for 450,000-7-0.6=750,000 B.t.u. per 24 hours, and the foregoing figure of 4,000,000,000 B.t.u. represents 5330 horse-power. Of this amount the blowing engine will require 3000 horse-power, leaving a surplus of 2330 horse-power for other purposes.
SEC. IIu.—Use of tunnel head gas for the production of power "by gas engines.—It has just been shown that a 400-ton blast furnace, after supplying its stoves, pumps, and hoisting engines, has 4,000,000,000 B.t.u. per day available for the blowing engines and for surplus. This is true for a steam equipment, but the figure is somewhat less for gas engines, since in the latter case the sensible heat of the gas is. of no value. This sensible heat is 1,500,000 out of a total of 16,000,000 B.t.u., so that by proportion the amount available for the gas engine plant will be 3,600,000,000 per day. Assuming that a gas engine will produce-one horse-power from 360,000 B.t.u. per day, there will be a total of 10,000 horse-power, or a surplus of 7000 horse-power after the blowing engine is supplied.
SEC. IIv.—General conclusions on the production of power from tunnel head gas.—The energy in one ton of coke is about 28,500,000 B.iu. The blast when heated to 1100° F. carries about 2,500,000 B.t.u. or 8 per cent, additional, making a total of 31,000,000 B.t.u. entering the furnace per ton of coke. Half of this energy is dissipated in the furnace, while the other half is contained in the tunnel head gas. The calorific value of the gas from a ton of coke is about 14,500,000 B.t.u., but the sensible heat at a temperature of 500° F. is 1,500,000 B.t.u., making a total of 16,000,000 B.t.u. or one-half the amount entering the furnace. Thus out of every 100 units of energy contained in the coke and the blast, 50 units come out in the gas, but of these 50 units it is necessary to send 17 units to the stoves, in order that 8 units may appear in the blast, it being assumed that the stoves have an eili-ciency of 50 per cent. This leaves 33 units for the production of power. If gas engines are used the sensible heat will not be available and only 30 units will be of use. In either case the amount is sufficient, when economical engines are used, to drive the blowing engine and pumps, and have a considerable surplus. In the case of a furnace using 400 tons of'coke per day, and equipped with